68 PHYSIOLOGY CHAP. 



animals, and raise their temperature to a given height, inde- 

 pendently of the variations of external temperature. From this 

 physiological standpoint it may be held that the muscle utilises 

 all the energy which it develops, either in the form of work or of 

 heat. 



XL A portion of the potential chemical energy liberated 

 during the activity of the muscle appears not as heat, but as 

 electricity. . 



A discovery of great importance in physics galvanism, and in 

 physiology animal electricity, originated in Galvani's observations 

 that muscles of a recently killed frog were thrown into convulsions 

 on closing the circuit between the muscles and the nerves by 

 means of two metals. From this Galvani concluded that the 

 muscles of the frog were normally charged like a Leyden jar, with 

 positive electricity inside and negative electricity outside each 

 muscle. Hence he assumed that on making connection between 



the inside and outside of a 

 muscle, a current was produced 

 which gave rise to the con- 

 traction. 



Volta at once recognised 

 that this interpretation was 

 erroneous, because the circuit 



FIG. 41. Galvani's second experiment, without i- 4 i 



metais. comprising two different metals 



in itself contained a source of 



electromotive force. The long controversy between Volta, who 

 affirmed the existence of metallic currents, and Galvani, who 

 maintained the contrary and endeavoured to explain everything 

 by muscle currents, is certainly one of the most remarkable 

 incidents in the history of experimental science. The contrary 

 statements of the two protagonists were true; their negations 

 were false. Volta's theory led to the discovery of the pile ; 

 Galvani's to the first demonstration that living tissues in general, 

 and the muscles in particular, may, under given conditions, be the 

 seat of the development of electrical currents. 



The observation of Galvani and his nephew Aldini was 

 based on the fact that contraction takes place in the muscles of 

 a recently killed frog, not only when a circuit is made between a 

 muscle and its nerve by a bridge consisting of two metals or even 

 of one metal, but also though in a less degree when the circuit 

 is made without any metal. This experiment, famous in the 

 annals of medicine, consists in laying the nerve-muscle preparation 

 of a frog upon a glass plate (Fig. 41), and bringing the surface of 

 the muscle into contact with the end of the freshly-cut nerve by 

 a glass rod. At the moment of contact the muscle contracts. 

 Eepeated and confirmed by Valli (1794) and Alexander v. 

 Humboldt (1798), this experiment underlies the general theory 



